There are no statistics for how many young people are taking drugs such as Ritalin, despite the fact that they have lots of side-effects. Photograph: Murdo Macleod

Leon Perry is in trouble for insulting his teacher. Fidgeting on a chair in the assistant head's office of Queen's Park community school (QPCS) in north London, the 13-year-old admits he skipped his medication the day the trouble started.

"I can get a bit hyperactive when I come off," he says. "I'll be honest, I can be violent. When I'm on my tablet, I think before I act, when I'm off, I think after. If teachers get on my nerves, I'll say what I want. When I'm on my tablet, I can't be bothered."

Leon has been taking Ritalin since he was diagnosed with attention deficit hyperactivity disorder (ADHD) when he was six. He's not alone. According to data obtained exclusively by Education Guardian under Freedom of Information legislation, there has been a 65% increase in spending on drugs to treat ADHD over the last four years. Such treatments now cost the taxpayer over £31m a year.*

With such a vast increase in figures, a growing number of academics are raising concerns that some teachers are either recommending these drugs as an easy alternative to dealing with bad behaviour, or simply turning a blind eye to those on medication when they should be investigating the root cause of their problems. In the worst cases, schools have been known to put significant pressure on students or their parents to seek the medication.

Take Leon. He insists he didn't want to start taking Ritalin. His mum didn't want him to, either. It was his last school that gave him an ultimatum: go on the drug and act with more respect, or leave the school. Seven years later, he still relies on Concerta Exel – a slow-release form of Ritalin – to control his moods.

"I know it helps me in some ways, but I hate taking it," he says, "There are days when I deliberately avoid it. You just don't feel yourself, you feel so drained out. It makes you feel disgusted and down. Like you've got no soul or something. My mum doesn't want me to take it, but what can she do? She wants me to get an education."

The drugs most frequently prescribed for ADHD are atomoxetine, dexamfetamine and methylphenidate3 – the last most commonly known by the brand name Ritalin.

Since ADHD first gained recognition as a medical condition in the mid-1980s, professionals have argued over the use of such drugs. Some believe they treat a legitimate problem. Others, such as education expert Dr Gwynedd Lloyd from the University of Edinburgh, refuse to acknowledge that ADHD is even a medical condition.

"You can't do a blood test to check whether you've got ADHD – it's diagnosed through a behavioural checklist," says Lloyd. "Getting out of your seat and running about is an example –half the kids in a school could qualify under that criterion. I know a lot of children have genuine difficulties, and some of these are biological, but most are social and cultural."

The growth in popularity of the drugs throws up serious questions for teachers. There may be a variety of causes for a child's challenging behaviour. Leon, for example, has had problems at home after his mother found it difficult to cope with him. But with huge pressure on time and resources – pressure that is only likely to increase in the current economic climate – teachers have fewer incentives to investigate the root causes of disruptive behaviour.

"Ideally, schools would prefer to offer intensive one-to-one support, but if the resources are limited – which they usually are – then we're pushed into a choice between medication or exclusion," says Tim Bown, assistant head at QPCS. "Hearing a student say that a drug 'takes away his soul' doesn't sit comfortably with us as a school, but permanent exclusion doesn't, either. There is no doubt his behaviour becomes more aggressive and disruptive when he comes off."

Although some doctors are more inclined to recommend the medication than others, Ritalin is fairly accessible through the NHS, although GPs have to refer the patient to a specialist before the initial prescription can be given. Many professionals do not take the recommended step of checking whether ADHD behaviour is exhibited at school as well as at home before signing off the medication.

Getting these decisions right is essential, because ADHD drugs can have significant side-effects, and the long-term effects of them on very young children whose brains are still developing remains unclear.

Twenty-one-year-old Mikaela Green knows all about the costs and benefits of Ritalin. Mikaela sought the diagnosis herself when she was 18, after severe disruption at school.

"The drugs helped me gain more control over my moods," she says. "I was a lot more focused and I didn't get distracted or distract others. I was far less impulsive – I wouldn't shout in lessons and my family life improved."

But after three years on the drug, she wants to come off. "They're not physically addictive, but I do feel dependent on them. If you've not had enough sleep they keep you going, if you're low they pick you up. I'm worried that if I stop taking them my world might fall apart.

"There are physical effects, too. For a good year they suppressed my appetite – and for an 18-year-old girl that's easy to abuse. I got involuntary muscle twitches because I wasn't sleeping or eating enough. I have to take sleeping pills now.

"Sometimes I think they make me more ADHD. If I take it in its pure form I get something I call 'Ritalin golden hour' when I can talk solidly the whole time, a bit like I'm on speed. I might have got some advantages out of the drug, but I wouldn't recommend it for younger children."

Schools like Queen's Park are doing their best to avoid medication. Employing several counsellors and psychotherapists, QPCS is participating in the Marlborough project, which is part of the Brent delivery of Targeted Mental Health in School (TaMHS). This invites challenging students and their parents to discuss poor behaviour once a week after school. Leon says the targets he is set there have helped him to improve. But as Bown points out, although there are only a handful of pupils at QPCS who need this service, it's still incredibly resource-intensive.

"All schools are facing cuts and it may well be these sorts of services – therapists, councillors, mentors – that will be the targets because, understandably, schools don't want to lose teachers."

This isn't the only economic incentive for choosing medication over other treatment methods. Parents whose children are diagnosed with ADHD are eligible for disability living allowance, and drugs companies can make huge profits from selling solutions to children's problems. According to Dr Lloyd, the explosion of ADHD diagnoses in the mid-1990s corresponded with an increase in marketing from US drugs companies, which felt they'd saturated the American market.

No records are currently kept about how many young people are on these drugs in the UK, and little research has been done into what the future might hold for them. Talk to Mikaela and Leon, however, and both of them want to reduce their intake.

"It's difficult to accept that without medication you're not good to be around," says Mikaela. "But I need to figure out what I'm really like. I might be worried about coming off, but I'm not sure I'm comfortable saying I am who I am because of medication."

Some names have been changed

* The figures of 65% and £31m do not include prescriptions dispensed in the private sector. They also do not include prescriptions that are dispensed from hospital pharmacies.

These figures include all prescriptions for methylphenidate, which are sometimes used to treat narcolepsy as well as ADHD. However,this would be for a very small number of patients, and is unlikely to distort the figures.

The figures may also include prescriptions for some older ADHD patients who have remained on the drugs since their youth, but researchers say the vast majority of these users are likely to be young people.